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FAIR VALUE MEASUREMENTS - Narratives (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
FAIR VALUE MEASUREMENTS
Impaired loans, carrying amount	$ 214,000		$ 214,000		$ 452,000
Net loss to adjust foreclosed assets to fair value	$ 4,000	$ 39,000	$ 18,000	$ 37,000

X

- Definition

Amount of increase (decrease) in the fair value of foreclosed assets recognized in the income statement.

+ References

No definition available.

+ Details

Name:	clst_ForeclosedAssetsGainLossOnFairValueAdjustmentsNet
Namespace Prefix:	clst_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Carrying amount of impaired loans.

+ References

No definition available.

+ Details

Name:	clst_ImpairedLoanCarryingAmount
Namespace Prefix:	clst_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- References

No definition available.

+ Details

Name:	us-gaap_FairValueDisclosuresAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration